The objective of this proposal is to prepare xenoantisera, in rabbits, reacting with defined membrane antigens of functional subclasses of human thymus-dependent lymphocytes (T cells). T lymphoblastoid lines, peripheral blood T cells, TM cells, and TG cells will initially be used to prepare immunogens. Blast and non-blast T cells, alloantigen binding and non-binding T cells, all isolated from primary and secondary mixed lymphocyte responses, and T blast cells responding to PPD will subsequently be used to prepare immunogens. Animals will be immunized with whole viable cells, cell membranes, and detergent-solubilized cell membranes. Solubilized membranes will be purified prior to immunization by negative selection, initially by removing irrelevant antigens shared by T and B lymphocytes, using affinity columns with bound rabbit antibodies to B lymphoblastoid cell membranes. Antigens common to all T cells will eventually be removed from solubilized membranes of T cell subclasses prior to immunization, by affinity chromatography using antibodies on T lymphoblastoid cells. Antisera will be analysed serologically and functionally on all T cell populations. The antisera will also be characterized in terms of the nature of the antigen with which they react, by immunoprecipitation of detergent-solubilized membranes from the T cell populations labeled internally or externally, followed by analysis using polyacrylamide gel electrophoresis in SDS an isoelectric focusing in 6 M urea. Electrophoretic variants of the antigens, and alloantigenic variants detectable serologically will ultimately be sought.